It is known to apply ellipsometers and polarimeters in the investigation of samples. Ellipsometers and polarimeters comprise a source of electromagnetic radiation, a polarizer, a stage for supporting a sample, an analyzer and a detector. There can also be present a compensator at some point between the polarizer and analyzer. Typically at least one of a present polarizer, analyzer and/or compensator is caused to rotate during collection of sample characterizing data during use.
It is also known to apply air bearings in motors that cause rotary motion, instead of more standard ball bearings and the like. Air bearings use a thin film or pressurized gas to provide a low friction load-bearing interface between surfaces which do not touch in use. The use of air bearings are less prone to problems of friction wear, particulates and lubricant handling etc., and offer advantages in precision positioning, especially in high speed applications. It is noted that the terminology “air” is to be read broadly to include dried atmospheric air, nitrogen, argon or any other gas of combination of gasses for the purposes herein.
For insight, it is noted that a distinction is made between what are termed “aerodynamic bearings”, which establish an air cushion through relative motion between a stator and moving parts, and “aerostatic bearings” in which a pressurized gas is continually entered during use, from an external source. It is the later aerostatic type of air bearing that is applied in the present invention.
While there is no known published literature or Patents pending or issued, it is rumored that KLA-Tencor has adapted motors for use in ellipsometers to use air bearings. There is one known expired U.S. Pat. No. 4,434,025 to Robillard, which mentions in passing, in Col. 9, Line 34 the terminology “air bearing”, and suggests use thereof in the monochromatic system therein, however, no description of a motor system comprising an air bearing is provided. If there are additional references pertaining to the use of air bearings in ellipsometers and polarimeters and the like, they are not known to the Inventors herein at this time.
It is noted that off the shelf “air bearing” containing motors are available from many manufacturers, however, the Inventors herein have found all standard motors containing air bearings to be unacceptable for application in ellipsometer and polarimeter and the like systems. The reason for this is that available air bearing containing motors, which have a centrally located hollow shaft through which in use a beam of electromagnetic radiation passes when applied in ellipsometry, and which can be fashioned to comprise a polarizer, analyzer or compensator in the path of said electromagnetic beam—make no provision for preventing a gas entered thereinto, which forms the air bearings, from exiting through the beam path. While for many applications this is a not a problem, in ellipsometry and polarimetry a changing environment in the path of a beam of electromagnetic radiation causes unpredictable and unacceptable changes in collected data. While application of air bearings in a motor system applied to cause a polarizer, analyzer and/or compensator to rotate in use is beneficial for many reasons, (not the least of which is that rotation speed is far more constant over time than when other type bearings are utilized), use of air bearings that allow gas entered thereinto to exit through a hollow shaft which provides access to said polarizer, analyzer and/or compensator, through which hollow shaft a beam of electromagnetic radiation is caused to pass in use, is unacceptable. As alluded to, the reason for this is that a change in the environment through which a beam of electromagnetic radiation passes adversely affects the ability to obtain data pertaining to a sample being investigated in that said data cannot be compensated for such random changes.
A need remains for ellipsometer and polarimeter and the like systems which comprise air bearings in a motor system therein which are applied to effect rotation of at least one selection from the group of:                polarizer;        analyzer; and        compensator;in use, which motor system provides a centrally located rotating hollow shaft through which a beam of electromagnetic radiation is caused to pass in use, which motor system is designed and applied such that gas entered thereinto to form the air bearings thereof does not exit through the hollow shaft during use.        